Study Unit 8: Manufactured non-cellulosic: polyester

Question 1

History

Answer 1

The initial work on polyester fibres was conducted by Dr W H Carothers. Polyester was actually developed before nylon, but when the polyamides showed more promise, research was concentrated on them and polyesters were set aside. British chemists also decided to continue research on polyester and in 1946 the polyester fibre, Terylene®, was introduced to the public.
DuPont’s polyester fibre came onto the market in the early 1950’s and was known as Dacron®. Since then many other polyester fibres such as Tergal®, Tetron®, Trevira®, Crimplene® and Kodel® have been placed on the market.

Question 2

Fibre production

Answer 2

Polyester is a manufactured polymer in which the fibre-forming substance is any long-chain synthetic polymer composed of at least 85% by weight of an ester of a substituted aromatic carboxylic acid. The principal raw material is ethylene, which is obtained from petroleum. Over 70 to 75% of polyester is produced by a continuous process using terephthalic acid and MEG (mono ethylene glycol). The other process is a batch process using dimethyl terephthalate and MEG. The process from thereon, is the same as for nylon.

Question 3

Fibre properties

Answer 3

Polyester has good resistance to solvents. Polyester is oleophilic (oil-loving) which means it absorbs oily substances and holds on to the oil tenaciously. Therefore polyester picks up oil stains easily and these are difficult to remove during laundering. Fabrics may be fine and soft or firm, according to fibre fineness, fabric construction and finishing. Fibres can be matte or lustrous depending on cross-section and additives.

Question 4

Physical structure

Answer 4

As with most other manufactured fibres, the length and diameter of polyester can be controlled. These produce a wide range of cross-sections, including, trilobal, octolobal, pentalobal, round, triangle and hollow. Filaments, textured and staple fibres are available. Different fibres can be produced to meet particular end-uses. Examples are high strength, flame resistant, heat resistant, high shrink, high crimp, antistatic, low melting and low pilling.

Question 5

Properties relating to durability

1. Abrasion resistance

Answer 5

Polyester fibres possess excellent abrasion resistance. However, the fibres are very strong and fabrics have a tendency to pill with prolonged use.

Question 6

2. Strength

Answer 6

The tenacity of polyester ranges from 31–39 cN/tex. Polyester does not lose much strength when wet and therefore requires less care during laundering.

Question 7

3. Flexibility

Answer 7

Polyester fibres have good flexibility.

Question 8

4. Elongation

Answer 8

Polyester has high elongation (40–45% elongation at break).

Question 9

Properties relating to comfort

1. Moisture absorption

Answer 9

Polyester fibres have low moisture absorption (0.4–0.5% moisture regain). A polyester garment is uncomfortable to wear in humid conditions but is quick drying. One can improve wicking properties using finishes and fibres which have different cross-sectional shapes. To improve comfort one can also blend with other fibres such as cotton which are able to absorb moisture. Polyester is inclined to build up static electricity (The use of a fabric softener in laundering may reduce static build up). Static can be a distinct disadvantage for dark fabrics because of the attraction of lint which spoils the appearance of the fabric.

Question 10

2. Heat conductivity

Answer 10

Although polyester fibres are better conductors of heat than acrylic fibres, their heat conductivity is still low. Yarn and fabric construction play a role in how cool or warm a polyester garment is. Blending can increase its comfort, for example, blending with wool increases warmth; and cotton coolness.

Question 11

Properties relating to appearance retention

1. Resiliency

Answer 11

Polyester fibres are highly resilient and recover excellently from creasing and wrinkling. Some polyester fibres have a recovery similar to that of wool at the higher elongations which helps explain the compatibility of wool and polyester blends.

Question 12

2. Dimensional stability

Answer 12

Polyester that has been heat-set will not stretch or shrink at temperatures lower than the heat-setting temperature (normally around 200 oC) Knitted polyester fabrics (and sometime woven fabrics) may shrink in the laundry if not properly heat-set. High temperatures in laundering can set creases.

Question 13

3. Elasticity

Answer 13

Polyester fibres are more elastic (76% recovery at 3% stretch) than cellulosic fibres but less elastic than nylon.

Question 14

Properties relating to care

1. Effect of alkalis

Answer 14

Polyester has good resistance to alkalis at room temperature.

Question 15

2. Effect of acids

Answer 15

Polyester has good resistance to acids at room temperature.

Question 16

3. Effect of sunlight

Answer 16

Polyester has good resistance to sunlight, hence the use for Terylene® for curtaining.

Question 17

4. Biological properties

Answer 17

Polyester is resistant to mildew, bacteria and insects.

Question 18

Durability

Answer 18

Excellent

Question 19

Abrasion resistance

Answer 19

Excellent

Question 20

Tenacity

Answer 20

Excellent

Question 21

Elongation

Answer 21

High

Question 22

Comfort

Answer 22

Low

Question 23

Absorbency

Answer 23

Low

Question 24

Heat conductivity

Answer 24

Low

Question 25

Appearance retention

Answer 25

High

Question 26

Resiliency

Answer 26

Excellent

Question 27

Dimensional stability

Answer 27

High

Question 28

Elastic recovery

Answer 28

High

Question 29

Care

Answer 29

Most items made from polyester can be dry-cleaned Most items made from polyester can be machine washed
Use warm water to minimise wrinkling and add a fabric softener to the final rinse cycle
Fibres may hold on to oily stains
Machine dry at low temperature setting
Remove articles as soon as the tumbling cycle is complete
If ironing is needed, use a moderately warm iron. Safe ironing temperate 163 oC
Resistant to chlorine bleach

Question 30

End Uses

Answer 30

A wide range of applications use polyester in clothing, home furnishings and industrial products.
 As a staple fibre, its biggest use is in blends with cotton. It is also blended with other fibres, such as wool.
 Filament yarns, usually textured, are used in apparel fabrics for dresses, blouses, ties, scarves and rainwear. They are also used in linings.
 Polyester on its own (hollow fibre) is used as a stuffing for duvets and pillows, toys and in jackets.
 High tenacity polyester is used for tent-roofing, tarpaulins, tire cords and geotextiles.
 Flame retardant varieties are used in hotel bedding, children’s nightwear, and
furnishings and upholstery in theatres and transport.